DESCRIPTION: (Adapted From The Investigator s Abstract): Complex behaviors and cognitive process such as those observed in humans and other primates are marked by increases in brain size, particularly in the forebrain. Such complexity is also characterized by an increase in the number of subdivisions, or areas, within the portions of the forebrain known as the neocortex and dorsal thalamus. These areas are interconnected to form intricate processing networks that ultimately generate complex functions such as perception, cognition, learning, and memory. The purpose of the present proposal is to investigate some aspects of forebrain expansion in the somatosensory system in two species of primates, macaque monkeys and marmoset monkeys, as part of the overall effort to understand how the multiple representations of the body surface in cortex are interconnected, and how the thalamus contributes to the organization, function, and maintenance of these representations. The first phase of these experiments is to examine the normal organization and connections of somatosensory cortex in anterior parietal, posterior parietal, and lateral somatosensory areas, with an emphasis on areas in the lateral sulcus. These experiments are designed to address several questions. First, how are the somatosensory cortex of the lateral sulcus, and those portions of posterior parietal cortex that are devoted to somatosensory processing, subdivided? Second, how do fields in the lateral sulcus differ in internal organization and stimulus preferences of neurons? Third, how are the individual somatosensory fields in the anterior and posterior parietal lobe, and lateral sulcus, precisely interconnected with other body part representations in other cortical fields, and with body part representations in different nuclei in the thalamus? In these experiments, multiple unit, electrophysiological recording methods will be used in combination with histological techniques to identify the number and organization of separate fields in the lateral sulcus in addition to SII and PV, and further explore areas 5, 7b and 3a. Using neuroanatomical tracers, studies of connections of these fields will be combined with electrophysiological mapping of expected target fields in the cortex and thalamus in an effort to correlate connection patterns with functional subdivisions, and with topographic maps within these subdivisions. The second phase of these experiments will focus on aspects of thalamic organization, and afferent projection patterns from the somatosensory thalamus to subdivisions of the neocortex. The questions addressed in these studies include What are the major subdivisions of the somatosensory thalamus, and how are they organized? What are the areal dimensions and laminar distribution of thalamic afferents to body part representations in different cortical fields? What is the relationship between thalamic afferents and intrinsic, ipsilateral and contralateral connections of electrophysiologically defined body part representations within the different cortical fields? These studies will help establish a primate model for somatosensory processing at higher levels of the nervous system, and provide information regarding the anatomical substrate for map organization and changes due to peripheral or cortical injury, by detailing the functional circuitry involved in clinical disorders involving somatic pathways.